Structure to form a load-bearing air cushion for a vehicle

ABSTRACT

An annular sealing assembly comprising an annular inflatable hanger on the underside of a load-bearing base and an annular sealing means on the underside of the hanger confines a loadsupporting air cushion that is continuously supplied with compressed air. The lower annular sealing means comprises a stack of resiliently deformable ring-shaped members with at least one flexible reinforcement ring incorporated therein to prevent radially outwardly ballooning of the annular sealing means and the annular sealing means is floatingly attached by a ring-shaped flexible member to a rigid ring-shaped plate on the underside of the hanger. Stability is promoted by supplying compressed air to the hanger continuously and continuously releasing air from the hanger. Noise is reduced by providing the underside of the annular sealing means with a flexible wear strip of lesser outside diameter than the annular sealing means.

United States Patent Vaughen Oct. 30, 1973 STRUCTURE TO FORM ALOAD-BEARING AIR CUSHION FOR A VEHICLE [76] Inventor: Jack F. Vaughen,26807 Spring Creek Rd., Palos Verdes Peninsula, Calif.

[22] Filed: Aug. 16, 1971 [21] Appl. No.: 166,930

Related U.S. Application Data [63] Continuation-impart of Ser. No.75,923, Sept. 28,

1970, abandoned.

Primary Examinerl(enneth H. Betts Assistant Examiner-J. M. McCormackAttorneyGeorge F. Smyth et al.

[57] ABSTRACT An annular sealing assembly comprising an annularinflatable hanger on the underside of a load-bearing base and an annularsealing means on the underside of the hanger confines a load-supportingair cushion that is continuously supplied with compressed air. The lowerannular sealing means comprises a stack of resiliently deformablering-shaped members with at least one flexible reinforcement ringincorporated therein to prevent radially outwardly ballooning of theannular sealing means and-the annular sealing means is floatinglyattached by a ring-shaped flexible member to a rigid ring-shaped plateon the underside of the hanger. Stability is promoted by supplyingcompressed air to the hanger continuously and continuously re leasingair from the hanger. Noise is reduced by providing the underside of theannular sealing means with a flexible wear strip of lesser outsidediameter than the annular sealing means.

49 Claims, 12 Drawing Figures PAIENIEMcI 30 I973 SHEET 3 OF 3 STRUCTURETO FORM A LOAD-BEARING AIR CUSHION FOR A VEHICLE CROSS-REFERENCE TOPATENT APPLICATION This application is a Continuation-impart of mycopending application of the same title Ser. No. 75,923, filed Sept. 28,1970, now abandoned.

BACKGROUND OF THE INVENTION My copending application Ser. No. 819,860filed Apr. 28, i969, and now abandoned discloses various embodiments ofthe load-bearing air-cushion apparatus in which an annular sealingassembly for confining an air cushion comprises an annular hanger whichinflates downwardly from 'the load-bearing base together with a flexibleresiliently yieldable annular sealing means which projects downward fromthe annular hanger into close proximity to the ground or support surfacealong which the apparatus travels.

One troublesome problem is to so construct such an air-suchion vehicleas to make it readily adaptable to changes in the loading of the vehicleas well as changes in the surface over which the vehicle moves. A givenvehicle may give excellent performance on a smooth surface but poorperformance on a rough or broken surface. It has also been found thatwhen a vehicle supported by a plurality of air cushions traverses arolling ground surface wherein the area of local changes in the groundsurface range upward in size to an area comparable to the area of asingle air cushion, it is highly desirable that each sealing assemblythat confines an air cushion act independently of all the other sealingassemblies to adapt itself to such local changes. Thus, while themajority of the sealing assemblies of an air cushion vehicle maymaintain substantially the same configuration to support the base of thevehicle, a particular sealing assembly traversing such a local change inthe ground surface should adapt itself independently to the local changeand thus change in configuration in such manner as to continue tosupport its share of the overall load. Too often the particular sealingassembly looses its efficiency to a serious degree.

The problem of making an air cushion vehicle readily adaptable tochanges in the load and changes in the terrain is complicated by thefact that under certain critical conditions difficult to predict, aconventional air cushion vehicle is excited to bounce or oscillatevertically in an uncontrolled manner that may become destructive. Suchdynamic instability is prone to occur when the operating conditionssuddenly change.

Another problem is to provide a sealing assembly SUMMARY OF THEINVENTION The invention teaches that in the construction of an aircushion vehicle having a plurality of annular sealing assemblies of thecharacter described, two provisions may be made for independentautomatic adjustment of the sealing assembly to a rolling surface wherethe area of a change in the configuration of the rolling surface is notsubstantially greater than the area of a single sealing assembly so thatonly one sealing assembly at a time is affected by the surface change.One provision is to make the lower annular sealing means sufficientlyresiliently yieldable to accommodate itself to rises or depressions ofthe ground surface that are of substantially smaller area than the areaof the sealing assembly. The second provision to make the sealingassembly automatically adaptable to rises or depressions of the groundsurface of areas comparable to the area of the sealing assembly is tomount a rigid ring-shaped plate on the underside of the downwardlyinflatable hanger in a floating manner with the lower dependent annularsealing means attached to the ring-shaped plate. Since the downwardlyinflated hanger is readily yieldable, it readily permits the floatingrigid ring-shaped plate to tilt relative to the load-bearing base of thevehicle in a universal manner and thus permits the dependent annularsealing means to tilt the ring-shaped plate to conform to a rise ordepression in the ground that is comparable in area to the area of thesealing assembly.

The invention further teaches that versatility in the adaptability ofthe annular sealing assembly to changing operating conditions may bepromoted by attaching the dependent annular sealing means to the rigidringshapedplate by suitable mounting means in a floating manner. Forthis purpose, a ring-shaped reinforcement sheet of flexible materialsuch as fabric is attached by its outer and inner circumferentialmargins to the rigid ring-shaped plate and the dependent annular sealingmeans is attached to the ring-shaped sheet intermediate its two marginswith sufficient slack in the sheet to permit the dependent annularsealing means to rock locally relative to the ring-shaped plate.

After considerable research and experimentation it is found that theoscillations of an annular sealing assembly of the describedconstruction that tend to occur unexpectedly under changing operatingconditions may be automatically damped and adequately controlled bycontinuously supplying the downwardly inflatable hanger with compressedair and simultaneously continuously releasing air from the interior ofthe hanger at a rate that is sufficiently reduced to maintain the hangerunder the desired pressure. Compressed air is supplied to the inflatablehanger by a pressure regulating valve and under some conditions of moreor less uniform operation, the provision for continuously releasing airfrom the interior of the hanger may comprise a simple orifice. In thepreferred practice of the invention, however, the pressure regulatingvalve is adjustable over a suitable range of pressures and the means forreleasing air from the hanger comprises a valve which also has asuitable range of adjustment.

The problem of constructing an annular dependent sealing means ofreadily yieldable material without a tendency for the annular sealingmeans to balloon out under the pressure of the air cushion is met byincorporating into the construction of the annular sealing means one ormore annular sheets of suitable stretchresistant material. Thering-shaped sheets act in hoop tension to maintain the circularcross-sectional configuration of the dependent annular sealing meanswithout limiting the ability of the annular sealing means to accommodateitself to changing operating conditions and especially to adjust itselfto changes in terrain.

A further feature of one practice of the invention is the concept ofemploying an inflated dependent annular sealing means whereby theresiliency and resistance to deformation of the sealing means may bereadily adjusted by changing the air pressure to which it is inflated.Preferably the inflated annular dependent sealing means comprises astack of inflated flexible tubes similar to the inner tubes ofautomobile tires with one or more of the ring-shaped flexible stretchresistant sheets incorporated into the stack.

A feature of the invention is that important factors in the functioningof the annular assembly may be readily and conveniently adjusted to meetvarious changes in the operating conditions including changes in theloading of the vehicle and changes in the terrain over which the vehicleoperates. One adjustable feature is provided by the adjustable pressureregulating valve that supplies compressed air to the inflated annularhanger. Another adjustable feature, of course, is provided by anadjustable valve when an adjustable valve is employed to vary the rateof which air is continuously released from the interior of the inflatedhanger. A third adjustable feature is provided by means to adjust therate at which compressed air is supplied to the air cushion thereby tovary the pressure of the air cushion. If an inflated dependent annularsealing means is employed, a still further adjustable feature isprovided by means to adjust the pressure that is maintained in theinflated sealing means. With these various adjustments readily availableto the operator, the operator may vary the behavior and operatingcharacteristics of the annular sealing assembly in accord with changesin the loading of the vehicle and changes in the character of thesurface that is traversed by the vehicle.

The features and advantages of the invention may be understood from thefollowing detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to beregarded as merely illustrative:

FIG. I is a somewhat diagrammatic view of an axial section of a sealingassembly that embodies the invention;

FIG. 2 is a fragmentary sectional view similar to FIG. 1 showing how asimple aperture or orifice may be employed instead of an adjustablevalve for continuous release of compressed air from the inflated hanger;

FIG. 2A is a view similar to FIG. 2 showing the inflatable hangerextended downward;

FIG. 3 is a diagrammatic view similar to FIG. 1 showing how the inflatedhanger adjusts itself to a local change in inclination of the supportingsurface that is traversed by the vehicle;

FIG. 4 is a view similar to FIG. 2 showing how the yieldable dependentannular sealing means accommodates itself to a local rise in the groundsurface, the area of the local rise being substantially less than thearea of the sealing assembly as a whole;

FIG. 5 is a sectional view similar to FIG. 4 showing how the dependentannular sealing means is free to cant relative to the underside of theannular plate to which it is attached;

FIG. 6 is a sectional view similar to FIG. 2 showing the construction ofan inflated annular dependent sealing means;

FIG. 7 is a somewhat diagrammatic view similar to FIG. 1 showing anaxial section of an alternate sealing assembly that embodies theinvention;

FIG. 7a is a fragmentary section illustrating a modification of thestructure shown in FIG. 7;

FIG. 8 is a flat pattern for an inflatable hanger showing itsconstruction from truncated angular segments;

FIG. 9 is a perspective view of the hanger in FIG. 8 showing thetruncated conical form it takes after edges of all segments are attachedtogether; and

FIG. 10 is a perspective view of the hanger in FIG. 9 after being formedinto its final shape and being attached to a flat flexible mountingbase.

DESCRIPTION OF SELECTED EMBODIMENTS OF THE INVENTION Referring to FIG. 1the presently preferred embodiment' of the invention is an annularsealing assembly that is mounted on the underside of a load-bearing base10 of a vehicle to enclose a space 12 for the formation of an aircushion which is continually supplied with compressed air from asuitable source through a duct 14 under the control of an adjustablethrottle valve 15. The annular sealing assembly which confines the aircushion comprises an annular downwardly inflatable hanger, generallydesignated 16, in combination with a dependent annular sealing means,generally designated 18, that is impervious to air flow therethrough andprojects downwardly from the hanger-into close proximity with the groundsurface 20.

The inflatable annular hanger 16 is enclosed by a suitable annular guardwhich not only serves the purpose of protecting the annular inflatablehanger from damage but also serves the purpose of supporting theload-supporting base 10 when the hanger is deflated. This annular guardmay comprise an outer circumferential cylinder 22 having a radiallyinwardly projecting flange 24 extending under the annular hanger and aninner circumferential cylinder 25 having a radially outwardly projectingflange 26 extending under the annular hanger. Thus the flanges of thetwo cylinders straddle the lower annular sealing means 18 and define anannular opening 28 through which the annular sealing means may retractupward into the interior of the annular guard to permit the two flanges24 and 25 to support the load-bearing base 10 when the annular hanger 16is deflated.

In the construction shown, the load-bearing base 10 is formed with adownwardly projecting circular rib 30 that conforms to the outercircumference of the annular sealing assembly and the base is alsoformed with a similar inner circular rib 32 that conforms to the innercircumference of the annular sealing assembly. The upper end of theouter cylinder 22 is flanged to form a rim 34' that registers with theouter circular rib 30 and the inner cylinder 25 is flanged to form asimilar rim 35 that registers with the inner circular rib 32. The outercircumferential margin of the envelope of the inflatable annular hanger16 is clamped between the outer rim 34 and the outer rib 30 and in likemanner the inner circumferential margin of the envelope is clampedbetween the inner rib 32 and the inner rim 35, the rims and ribs beinginterconnected through the material of the envelope by suitablefastening means to clamp and secure the marginal portions of theenvelope in a fluid tight manner. The envelope of the inflatable annularhanger 16 may be made of any suitable flexible air tight material suchas nylon fabric impregnated with suitable material to prevent a leakagetherethrough and may be formed with outer and inner circumferentialbeads 36 for more effective retention of the marginal portions of theenvelope.

Suitably mounted on the underside of the annular inflatable hanger 16 ina floating manner is a rigid ringshaped plate or member 40 whichconforms to the annular configuration of the annular hanger and whichmay, if desired, be of substantial radial dimension to overhang both theouter circumferential flange 24 and the inner circumferential flange 26of the annular guard. In such a construction, the annular guard incombination with the rigid ring-shaped plate 40 completely shields theenvelope of the annular hanger 16 from damage and particularly fromrupture by any loose material that may be projected upwardly from theground surface 20.

The rigid ring-shaped plate 40 may be attached to the envelope of theinflatable annular hanger in any suitable manner but preferably only thecentral circumferential region of the ring-shaped plate is directlyattached to the envelope. In the construction shown, a relatively narrowrigid ring 42 is positioned inside the envelope and is attached to therigid ring-shaped plate 40 by suitable screws 44 that extend through thematerial of the envelope, the envelope being clamped between the ring 42and the ring-shaped plate. By virtue of this construction, loweringofthe rigidring-shaped plate from the position shown in FIG. 1 byincreased inflation of the annular hanger 16 results in the envelope ofthe annular hanger peeling away from the upper surface of the rigidring-shaped plate both inside and outside of the narrow ring 42 asindicated in FIG. 2A. It is also to be noted that in the event that therigid ringshaped plate 40 rises from the position shown in FIGS. 1 and 2because of decreased inflation of the annular hanger 16, the envelope ofthe hanger forms two bulges around the outercircumference and innercircumference respectively of the rigid ring-shaped plate and ye will beprotected by the annular guard.

The lower annularsealing means 18 may be connected to the rigidring-shaped plate 40 in various ways in various practices of theinvention but a feature of the present embodiment is the concept ofattaching the annular sealing means to the ring-shaped plate by asuitable mounting means in what may be termed a floating manner in thesense that the annular sealing means has freedom to rock locallyrelative to the rigid ring-shaped plate as well as slight freedom tomove downwardly from the rigid ring-shaped plate. For this purpose theupper annular end of the annular sealing means 18 is bonded to amounting means in the form ofa ringshaped flexible sheet 45 and thering-shaped sheet is bonded to the rigid ring-shaped plate 40 along oneor both of its outer and inner circumferential margins. In theconstruction shown, both the outer and the inner circumferential marginsof the ring-shaped sheet 45 are bonded to the rigid ring-shaped plate 40with sufficient slackness to permit the ring-shaped sheet to give theannular sealing means the desired freedom for movement relative to therigid ring-shaped plate. The freedom for the annular sealing means 18 torock locally relative to the rigid ring-shaped plate 40 is illustratedby FIG. 5. The ring-shaped flexible sheet 45 may be made of the samematerial as the envelope of the inflatable annular hanger 16.

The annular sealing means 18 may be of any suitable resilientlydeformable air-tight construction to confine the air cushion and at thesame time to accommodate itself to local changes in the ground surface20. In this instance the annular sealing means is made of foamedelastomer which may be of closed cell structure or may be of open cellstructure with an outer air-tight coating.

The underside of the annular sealing means 18 is provided with aflexible annular wear strip 46 which is chamfered at its outer and innercircumferential edges as shown to facilitate passage over irregularitiesin the ground surface 20 and also over loose material on the groundsurface. The wear strip may be made of any suitable flexibleabrasion-resistant material that is compatible with the surface overwhich the air cushion vehicle is operated. For example, if the groundsurface is machined troweled concrete or linoleum, the wear strip may bemade of Neoprene coated with Teflon. On the other hand, if the groundsurface is highly abrasive asphalt the wear strip may be a felt-likematerial such as commercial indoor-outdoor carpeting.

It has been found that when a dependent resiliently deformable annularsealing means of the character described is employed, there is atendency for the air that escapes radially outwardly under the annularseal to induce vibration of. the material of the annular seal near itsouter lower edge. This vibration is commonly in the audible range andthus creates disturbing noise. It has been found that if the wear strip46 is'of solid elastomer and projects radially outwardly to the outercircumference of the annular seal or beyond the outer circumference, theouter edge of the wear strip vibrates to create this noise. If such awear strip is of smaller outside diameter than the annular seal so thatthe wear strip is set back radially from the outer circumference of theannular seal as indicated in the drawings, the noisecreating vibrationdoes not occur because the downward pressure of the body of the annularsealing means destroys the freedom of the wear strip to vibrate. If,however, the outer edge of the wear strip is set back too far from theouter circumference of the annular sealing means the lower edge ofsponge member 48 may bulge downward into contact with the floor and beresonated to cause the troublesome noise.

Apparently there is some relation between the degree to which the wearstrip should be set back and the thickness of the wear strip. Forexample, if the wear strip is one-eighth inch thick, the set back shouldbe approximately one-eighth inch. It has been further found that if thewear strip is made of solid elastomer or plastic as distinguished from awear strip made of felt-like material, it may be necessary to chamferboth of the outer circumferential and inner circumferential edges of thewear strip. In some instances setting back the outer circumferentialedge of the wear strip is sufficient to eliminate the noise withoutchamfering the wear strip. In other instances chamfering the wear stripis sufficient without setting back the wear strip from the outercircumferential edge of the annular sealing means. In most instances,however, it is necessary both to set back the wear strip from the outercircumference of the annular sealing means and to chamfer both the outerand inner edges of the wear strip.

To make the wear strip 46 readily removable for replacement, it isbonded in place by commercial contact cement so that it may be peeledoff without disturbing the rest of the annular sealing means.

A feature of the invention is the concept of incorporating into thestructure of the-resiliently deformable annular sealing means 18suitable provision to keep the annular sealing means from ballooningradially outwardly under the pressure of the confined air cushion. Forthis purpose one or more flat flexible rings of stretch-resistant sheetmaterial is incorporated in the construction of the annular sealingmeans to function under hoop tension to maintain the circularcrosssectional configuration of the annular sealing means. The sheetmaterial of the reinforcing rings may be Dacron sailcloth, or Mylarsheet for example.

In the structure shown in FIG. 1 the annular sealing means 18 comprisesa stack of two relatively thick sections or rings 48 of the foamedelastomer with a reinforcement ring 50 of sailcloth or Mylar interposedbetween the two sections and bonded thereto and with a second ring 52 ofsailcloth or Mylar interposed between the lowermost section 48 and thewear strip 46. In the preferred practice of the invention, the uppermostsection 48 is made of much softer resilient cellular material than anysection below it so that it is primarily the uppermost section thatyields in compression to accommodate a local rise in the ground surface.The lowermost section 48 should be much less soft to meet the previouslydiscussed noise problem.

The envelope of the annular hanger 16 is inflated in completeindependence of the compressed air that'is supplied through the valve tothe air cushion inside the annular sealing assembly. The problem ofcombating bounce or uncontrolled oscillation of the inflated annularhanger 16 is solved by continually introducing compressed air into theenvelope of the annular hanger and simultansously continuously releasingair from the interior of the annular hanger at a sufficiently restrictedrate to maintain the desired pressure in thehanger. In FIG. 1 thispurpose is served by continuously introducing compressed air into theinterior of the annular hanger through a duct 54 under the control of apressure regulating valve 55 and at the same time continuously releasingair from the interior of the annular hanger through a short dischargeduct 56 under the control of an adjustable throttling valve 58.

The function of the discharge duct 56 in damping out theoscillations'may be understood when it is considered that the rate atwhich air is released through the valve 58 varies with the rate at whichthe hanger envelope is contracted by the repeated oscillations. Thepressure that prevails inside the hanger is determined by the adjustmentof the pressure regulating valve 55.

Tests have demonstrated that for each air cushion pressure correspondingto a particular loading of the vehicle there is an optimum pressureinside the inflatable hanger and when the pressure regulating valve 55is set to provide this optimum pressure,- the friction between the wearstrip 46 and the ground and the required rate of air flow to the aircushion are both minimized. Thisoptimum pressure may be quickly foundempirically to cause the air cushion vehicle to operate at its greatestefficiency as measured by the ratio between the weight ofthe imposedload and the horsepower required to maintain the air cushion.

In the functioning of the throttle valve 58 as pneumatic damping meansfor the annular sealing assembly, the degree to which the valve isopened depends upon the efficiency of the lower annular sealing means 18in minimizing the escape of air from the air cushion between the groundsurface and the wear strip 46. If the vehicle operates over a verysmooth floor with a rela tively low rate of air flow into the aircushion and, of course, a relatively low rate of air discharge under thewear strip 46, the opening required for the valve 58 is greater thanwhen the vehicle is operating over a relatively rough ground surfacewith greater leakage under the wear strip 46. In any event, once thepressure regulating valve 55 is set to provide the proper pressure inthe hanger and the throttling valve 58 is set to damp out verticalbounce, the setting of the valve 15 can be varied widely to provide awide range of rates of air flow into the air cushion without excitingdynamic instability. Thus the operator is free to select a desired rateof flow to the air cushion without concern for possible excitingvertical bounce.

FIG. 2 illustrates the fact that a simple aperture 56a in theload-bearing base 10 may be substituted for the duct 56 and valve 58 forcontinuous release of air from the hanger 16.

In FIG. 3 it is assumed that either a rise or a depression in the groundsurface has created a local slope 60 of an area comparable to the areaof the annular sealing assembly so that only the one sealing assemblyofthe plurality of sealing assemblies is effected by the slope. In thatevent the particular annular sealing assembly that traverses the slope60 accommodates itself to the slope independently of all of the otherannular sealing assemblies of the air cushion vehicle and thisaccommodation is accomplished primarily by tilting of the rigidring-shaped plate 40. In FIG. 3 the ring-shaped plate 40 is tilted to anattitude that is substantially parallel with the slope 60. By virtue ofthe capability of the annular sealing assembly to accommodate itself tosuch a local change in the configuration of the ground surface, theannular sealing assembly continuesto bear its share of the overall loadon the vehicle.

FIG. 4 shows how the capability of the annular sealing assembly 18 forresilient deformationmakes it possible for the annular sealing means toaccommodate itself to relatively small rises or depressions in theground surface. FIG. 4 shows how the annular sealing means 18accommodates itself to a relatively small rise 62 largely by localvertical compression of the annular sealing means 18,'the accommodationto the small rise being accomplished by yielding action of the annularsealing means, the rigid ring-shaped plate 40 preventing local effect onthe hanger 16. In FIG. 4 the resilient yielding action of the annularsealing means 18 is primarily in the uppermost annular section 48.

' FIG. 6 shows how the annular sealing assembly may be modified toprovide control over the resiliency or spring rate of the annularsealing means. The construction shown in FIG. 6 is largely identicalwith the previously described structure as indicated by the use ofcorresponding numerals to indicate corresponding parts. In.FIG. 6 theannular sealing means, generally designated 18a, comprises a stack ofinflatable rings 64 which are structurally similar to in'nertubes usedin automobile tires. Air to keep thetubes 64 inflated is supplied by aduct 65 under the control of a pressure regulating valve 66, the ductbeing continued as a flexible tube 68 inside the hanger 16a. Theflexible tube 68 terminates at a port 70 into the uppermost tube 64, aport 72 placing the uppermost tube in communication with theintermediate tube and a port 73 placing the intermediate tube incommunication with the lowermost tube. On the underside of the lowermost tube 64 a previously described wear strip 46a is removably mountedin the previously described manner.

In the construction shown, a first reinforcement ring 74 of sailcloth orMylar is interposed between the uppermost tube 64 and the intermediatetube; a second similar reinforcement ring 75 is interposed between theintermediate tube and the lowermost tube; and a third reinforcement ring76 is interposed between the lowermost tube and the wear strip 460. Hereagain, pneumatic damping is preferably provided to prevent instabilityor uncontrolled bounce and for this purpose, at least one of the threetubes 64 is provided with a vent aperture 78 that opens to theatmosphere on the outer circumference of the annular sealing means 18a.

Referring to FIG. 7, another embodiment of the invention is an annularsealing assembly that is mounted on the underside of a load-bearing base100 to enclose a space 12 for the formation of an air cushion which iscontinually supplied with compressed air from a suitable source throughorifice 79. As in the first embodiment, the annular sealing assemblywhich confines the air cushion comprises an annular downwardlyinflatable hanger, generally designated 16, in combination with adependent annular sealing means, generally designated 18, that isimpervious to air flow therethrough and projects downwardly from thehanger into close proximity with the ground surface 20.

The outer periphery of annular hanger 16 is enclosed by a suitableannular guard 22a which not only serves the purpose of protecting theannular inflatable hanger from damage but also serves to attach theouter edge of hanger 16 to the underside of load bearing base a in anairtight manner. The underside of base 10a is also fitted with adownwardly projecting inner cylindrical ring 80 and an intermediatecylindrical ring 81 which are concentric with each other and with outerannular guard 22a. The lower edge of cylindrical ring 81 is attached inairtight manner to the outerperiphery of a horizontal circular baseplate 82. The lower edge of cylindrical ring 80 is attached in airtightmanner to the rim of a circular hole in the center of base plate 82.Therefore, load bearing base 100, concentric cylindrical rings 80 and 81and circular base plate 82 together form an annular airtight chamber 83.This structure also provides support for the load beaing base 10a whenno air is supplied to generate a lifting air cushion underneath itthereby preventing the dead weight from crushing the seals 18. The innerperipherial edge of inflatable hanger 16 is attached to the lowerportion of the intermediate cylindrical ring 81 by a suitable airtightband tension clamp 84 so that the inflatable hanger completes an annularchamber .85 that surrounds the annular chamber 83.

Experiments have demonstrated that dynamic stability of a lifting aircushion of this type is enhanced if the enclosed volume inside thehanger is made as large as possible compared to the volume of thelifting air cushion. This volume ratio is improved in the presentembodiment of my invention by interconnecting the annular chamber 83 andthe annular chamber 85. This is accomplished by providing a number ofopenings 86 in cylindrical ring 81. Air can then flow freely between theannular chamber 83 and the annular chamber 85 through holes 86 asindicated by the arrows. Therefore, the volumes enclosed by annularchambers 83 and 85 function as a single volume in this embodiment of myinvention.

FIG. 7 shows one method of introducing compressed air into annularcavity 83. In this method, compressed air is allowed to flow asindicated by the arrow from the air cushion cavity 12 into annularchamber 83 through a small fixed diameter orifice 87 drilled through thewall of cylindrical ring 80. FIG. 7a illustrates an alternate method inwhich compressed air is allowed to flow as indicated by the curved arrowfrom the air cushion cavity 12 into annular chamber 83 through anadjustable hanger feed valve 88 which is mounted on a short tubeprojecting through the wall of cylindrical ring 80.

In the embodiment of the invention shown in FIG. 7, the outer wall ofinflatable hanger 16 is fitted with one or more small fixed diameterbleed holes 89. Air can flow from the interior of the hanger 85 to theatmosphere through-these bleed holes as indicated by the arrow. Bleedholes 89 are preferably located in the lower portion of hanger 16 asshown so that they are closed by the flat floating ring during initialbuildup of the air cushion in the space 12 and remain closed until theair cushion expands to almost its full operating height. Thisfacilitates initial inflation of the hanger during liftoff as will beexplained.

When the load-bearing air cushion assembly shown in FIG. 7 is at restand idle with no air being supplied to its lifting air cushion, bottomplate 82 of annular chamber 83 rests on the floor surface 20 to supportthe load-bearing base 10a, but at that time the dependent annularsealing means 18 is pressed firmly to the floor and the sponge portions48 of the seal are slightly compressed.

When lifting air is introduced through orifice 79 as indicated by thearrow it enters the passage 90 that is formed by the cylindrical ring80. Bottom plate 82 of the annular chamber 83 has a number of radialchannel-like depressions 91 in its lower surface which allow the air topass from passage 90 radially outward to enter the air cushion space 12.At the same time air can also flow into annular chamber 83 through fixedorifice 87. As previously explained, -annular chamber 83 and the annularchamber of the hanger 16 are interconnected by a number of relativelylarge holes 86. Therefore, as air pressure builds up in annular chamber83 it simultaneously builds up in the annular hanger chamber 85.However, it should be recognized that when hanger 16 is being initiallyinflated in this manner, the load-bearing base 10a is supported by thebottom wall 82 of annular chamber 83 and floating ring 40 is pressedupward against the underside of the loadbearing base by the resilientcompression of sponge portions 48 of the annular sealingmeans 18.

To facilitate inflation of the annular hanger chamber 85, the undersideof the load-bearing base 10a is equipped with one or more raised annularridges 92 of approximately the diameter of the annular sealing means 18.These ridges prevent floating ring 40 from pressing flat against theunderside of load-bearing base 10a. To facilitate radial movement of airinto hanger cavity 85 during initial inflation, the annular ridges 92are formed with a radial slot 93. Thus, even though floating ring 40 ispressed upward against the annular ridges 92, air can flow through slots93 to inflate the total width of hanger cavity 85.

As previously explained, in the absence of an air cushion in the space12, floating ring 40 closes the small hanger bleed holes 89. Then whenlifting air is supplied as described above, the hangers 16 inflate andthe air cushion in space 12 expands to the normal operating conditionshown in FIG. 7. Air pressure in the air cushion cavity 12 automaticallyrises to the level required to lift the load being carried on top of theloadbearing base a. Air pressure in the annular hanger chamber 85 alsorises until it reaches some equilibrium value which is a fixedpercentage of the air cushion pressure.

In my invention the ratio of hanger pressure to air cushion pressure ispreferably in the range 0.50 to 0.75. The exact value of this ratio isestablished by the relative sizes of bleed orifices 89 compared tohanger feed orifice 87 in FIG. 7 or in FIG. 7a by adjustment of hangerfeed valve 88. The fact that air pressure in air cushion cavity 12 ishigher than the air pressure in the annular hanger chamber 85 producesthe upward ballooning of the radially inner portion of the envelope ofhanger 16 as shown in FIG. 7. It should be noted that bleed orifices 89also serve to provide hanger damping to prevent dynamic bounceinstability of the air cushion during operation. Thus, in thisembodiment of my invention, hanger bleed orifices 89 replace hangerbleed valve 58 shown in FIG. 1 and hanger bleed orifice 56a shown inFIG. 2.

In FIG. 7 an alternate method is shown for attaching the envelope of aninflatable hanger 16 to a floating ring 40. The centerportion of hanger16 is attached to a flat ring of cloth 94 by two concentric rows ofstitches 95 and 96. In the annular area 104 between these rows ofstiches the envelope of hanger 16 is preferably also bonded orvulcanized to cloth ring 94 to produce an airtight connection. Clothring 94 is then bonded in airtight manner to the top surface of floatingring 40. Thus a central concentric annulariportion of the envelope is,in effect, bonded to a corresponding central concentric portion of thefloating ring 40.

It is apparent that the hanger bleed orifices 89 and the cloth coveredfloating rigid ring 40 function as a valve that is responsive to thepressure in the hanger 16, the valve closing when the pressure isrelatively low and opening automatically when the pressure is relativelyhigh, and when the valve isopen it functions. as

damping means.

For most efficient operation of the air seal it is imperative thatinflatable hanger l6 bear down on the top surface of floating ring 40with uniform pressure around its entire periphery. The preferredconstruction of the hanger to accomplish this is shown in FIGS. 8, 9 and10. A blank for the inflatable hanger is shown in FIG. 8 and isconstructed from an arbitrary number of truncated segments 97-as shown.Eachof these segments is made from cloth which has been coated to makeit impervious to airflow therethrough. The picshaped segments are cutfrom the cloth so that the threads of the cloth are oriented paralleland perpendicular to the centerline of each segment as shown at 98.Edges of adjacent segments are overlapped as indicated at 99 and may beattached together by any flexible airtight attachment means such asbonding and stitching or vulcanizing.

When the free ends 100 and 101 of the blank in FIG. 8 are overlapped andjoined together, the hanger takes the shape of a truncated cone as shownin FIG. 9. The edge 102 of this cone which has the smaller circumferencecan be displaced axially into the same plane as the edge 103 which hasthe larger circumference. This displacement is accomplished by foldingthe cone into a semi-toroidal shape as shown in FIG. 10. The lowerextremity 104 of this semi-toroidal shape is then attached by stitchingand bonding or vulcanizing to cloth ring 94 as previously described.Although the configuration in place of the structure in FIG. 10 iscircular it may be oblong in some practices of this invention.

Annular sealing means 18 is flexibly attached to rigid floating ring 40by a mounting means 45a in the form of a ring-shaped sheet as previouslydescribed for the first embodiment of my invention. Required loosenessin the ring-shaped sheet 45a can be provided by making it of downwardlybowed cross section, preferably, by

forming it into a truncated cone using the method just described for theinflatable hanger l6 and shown in FIGS. 8 and 9. However, the geometryof the pieshaped flat segments is adjusted to produce a much shallowercone for the ring-shaped sheet or mounting means 45a than for the deephanger 16. Also, the cone can be formed from a smaller number ofsegments since the mounting means 45a is not inflated and uniformstretch is not critical. However, to prevent entrapv ping air in themounting means 45a which would interfere with its flexibility when it ismounted to the underside of floating ring 40, the outer half of themounting means is preferably provided with a number of ample circularvent openings 105. These vent openings allow the interior of mountingmeans 450 to always operate at atmospheric pressure and air can freelypass in and out of the hanger during operation. Thus, the annularsealing means 18 is attached'to the envelope of the hanger 16 by avented hollow flexible structure.

Since mounting means 45a is constructed with considerable looseness orslack as described above, it is desirable to install an additional flat,flexible reinforcing tension ring 106 between the mounting means and theupper sponge portion 48 of annular sealing means 18. This upper tensionring 106 has the same diameter as intermediate tension ring 50 and lowertension ring 52 of the annular sealing means 18 and serves the samepurpose of preventing radial expansion of annular sealing means by thehigh pressure of the air cushion in the air cushion space 12.

I claim: 1. A fluid cushion device comprising: base means to receiveloads, at least one sealing assembly to confine a fluid cushion, 7 saidsealing assembly comprising an annular hanger projecting from the basemeans and annular structure below the hanger and cooperative therewithto enclose the fluidjcushion, said hanger being made of flexible sheetmaterial and being inflatable for vertical resilient deformability toyieldingly urge said annular structure away from the base means, saidannular structure being of less radial dimension than the hanger andbeing positioned within an annular area defined by the hanger, thehanger when inflated having an outer annular flexible sheet wallextending from the base means radially inwardly to the annular structureto act under tension to oppose lateral displacement of the annularstructure in one respect relative to the base means, and having an innerannular flexible sheet wall extending from the base means radiallyoutwardly to the annular structure to oppose lateral displacement of theannular structure in the opposite respect relative to the base means tostabilize the annular structure relative to the base means without needfor linking the annular structure directly to the base means; and

means to inflate said hanger and to supply pressurized fluid to thefluid cushion, said annular structure including a rigid ring-shapedplate attached to the underside of the hanger,

said annular structure further including resiliently deformable annularsealing means projecting downward from the ring-shaped plate to closeproximity to the ground surface under the device.

2. A combination as set forth in claim 1 which includes:

guard means fixedly mounted on the underside of the base to protect theinflatable hanger and to support the base when the hanger is deflated,

said guard means including an outer circumferential flange extendingunder the hanger from the outer circumference thereof and an innerannular flange extending under the hanger from the inner circumferencethereof,

said two flanges straddling said annular sealing means and defining anannular opening to permit upward retraction of the annular sealing meanswhen the hanger is deflated to cause the base to be supported by theguard means. 3. A combination as set forth in claim 2 in which saidring-shaped plate overhangs both of said flanges to cooperate with theflanges to shield the inflatable hanger from below.

4. A combination as set forthin claim 2 in which said guard meanscomprises:

only a central circumferential portion of the rigid ring-shaped plateattached to the inflatable hanger so that progressive downward movementof the rigid ring-shaped plate relative to the base causes theinflatable hanger to peel away from the rigid ring-shaped plate as therigid ring-shaped plate approaches its lower limit position andprogressive upward movement of the rigid ring-shaped plate eventuallycauses the hanger to bulge downward from the rigid ring-shaped plate.

5. A combination as set forth in claim 2 in which said ring-shaped plateis of lesser radial dimension than the inflatable hanger and the guardmeans provides clearance adjacent both the outer circumferential edgeand the inner circumferential edge of the ring-shaped plate for downwardbulging of the inflatable hanger inside the guard means.

6. A combination as set forth in claim 1 in which only a centralcircumferential portion of the rigid ringmeans to release aircontinuously from the hanger at a sufficiently reduced rate to keep thehanger inflated, whereby any tendency for the hanger to expand andcontract for bouncing action is dampened because the rate of release ofair from the hanger by said releasing means varies with the rate ofcontraction of the hanger.

8. A combination as set forth in claim 7 in which said means to releaseair from the hanger is an adjustable valve.

9. A combination as set forth in claim 7 in which the means to supplyair to the inflatable hanger comprises an adjustable pressure regulatingvalve operable to maintain a selected pressure in the hanger.

10. A combination as set forth in claim 9 in which said means to releaseair from the hanger is an adjustable valve. 7

11. A combination as set forth in claim 7 in which the I annular sealingmeans is inflatable and which includes shaped plate is attached to theinflatable hanger so that means to supply compressed air continuously tothe inflatable annular sealing means for inflation thereof and means tocontinuously release air from the inflatable annular sealing means at arate to keep the annular sealing means inflated.

12. A combination as set forth in claim 1 in which said annular sealingmeans is inflatable and which includes means to keep the annular sealingmeans inflated. v

13. A combination as set forth in claim 12 in which said means to keepthe annular sealing means inflated comprises means to supply compressedair continuously to the annular sealing means and means to release aircontinuously from the annular sealing means at a rate to maintaininflation of the annular sealing means.

14. A combination as set forth in claim 13 in which the means to supplycompressed air continuously to the annular sealing means comprises anadjustable pressure regulating valve.

l5.-A combination as set'forth in claim 1 in which said annular sealingmeans is floatingly mounted on the underside of the rigid ring-shapedplate.

16. A combination as set forth in claim 15 in which a ring-shapedflexible sheet under the rigid ring-shaped plate is attached to therigid ring-shaped plate adjacent at least one of the outercircumferential margin and the inner circumferential margin of thering-shaped sheet, the intermediate circumferential portion of theringshaped sheet being free from attachment to the ring shaped plate, 1

the upper annular surface of the annular sealing means being bonded totheintermediate circumferential portion of the ring-shaped sheet.

17. A combination as set forth in claim 16 in which the ring-shapedflexible sheet is attached to the ringshaped plate both adjacent theouter circumferential margin of the ring-shaped sheet and the innercircumferential margin of the ring-shaped sheet, the intermediatecircumferential portion of the ring-shaped sheet being slack to permitthe annular sealing means to cant locally relative to the rigidring-shaped plate.

18. A combination as set forth in claim 1 in .which said annular sealingmeans comprises a stack of substantially ring-shaped resilientlydeformable members; and

in which at least one flexible ring-shaped sheet is interposed betweentwo of said members to act under hoop tension to oppose radially outwardballooning of the annular sealing means.

19. A combination as set forth in claim 18 in which a resilientlyflexible wear strip is removably attached to the underside of the lowestmember of the stack.

20. A combination as set forth in claim 19 in which a flexibleabrasive-resistant wear strip is mounted on the underside of the stack;and

in which a ring-shaped reinforcement sheet is interposed between thelowermost ring-shaped member of the stack and said wear strip.

21. A combination as set forth in claim 18 in which the ring-shapedmembers of the stack include relatively thick members made ofresiliently deformable cellular elastomer.

22. A combination as set forth in claim 21 which includes at least onering-shaped sheet in hoop tension between two of the relatively thickmembers of the stack.

23. A combination as set forth in claim 1 which includes a wear strip ofresilient abrasive-resistant material mounted on the underside of theannular sealing means,

said wear strip being set back radially from the outer circumference ofthe annular sealing means to minimize noise created by the escaping ofair under the wear strip.

24. A combination as set forth in claim 23 in which the wear strip ismade at least largely of elastomeric material.

25. A combination as set forth in claim 24 in which the underside of thewear strip is coated with a low friction wear-resistant plastic.

26. A combination as set forth in claim 23 in which said wear strip isconstructed of felt-like fabric.

27. A combination as set forth in claim 23 in which the wear strip' isreleasably mounted by pressuresensitive adhesive.

28. A combination as set forth in claim 23 in which the wear strip ischamfered along its outer circumferential edge.

29. A combination'as set forth in claim 23 in which the wear stripischamfered along its inner circumferential edge. I

30. A combination as set forth in claim 1 in which an upper annularportion of said annular sealing means is resiliently deformable and issubstantially softer than the remainder of the annular sealing means tocause the annular sealing'means to accommodate itself to a local rise inthe ground surface primarily by compression of said upper annularportion.

31. A combination as set forth in claim 30 in which an annular strip ofresilient abrasion-resistant material is mounted on the underside of theannular sealing means, said wear strip being set back radially from theouter circumference of the annular sealing means.

32. A combination as set forth in claim 30 in which said annular sealingmeans comprises a stack of substantially ring-shaped resilientdeformable members, the uppermost of said ring-shaped members being madeof cellular elastomer.

33. A combination as set forth in claim 32 in which the ring-shapedmembers of the stack below the uppermost member are made of cellularelastomer.

34. A combination as set forth in claim 1 in which a central concentricannular portion of the envelope of the hanger is united with acorresponding ring-shaped sheet and the ring-shaped sheet in turn isbonded to the upper surface of the rigid ring-shaped plate.

35. A combination as set forth in claim 1 in which a cylindrical wallextends downward from the base means adjacent the inner periphery of theinflatable hanger and in which the inner peripheral edge of the envelopeof the hanger is attached to said cylindrical wall at a level spacebelow the base means to increase the effective volume of the envelope.

36. A combination as set forth in claim 1 which includes a chamber onthe underside of the base means, said hanger surrounding the chamber andbeing in fluid communication with the chamber for air flow between thechamber and the hanger.

37. A combination as set forth in claim 36 which includes a passageextending downward from the base means to supply air to the air cushion;

in which said chamber is an annular chamber surrounding said passage;and

in which said passage is in communication with said chamber to supplyair to the hanger through the chamber. 38. A combination as set forth inclaim 37 in which thewall of said passage has a port for fullcommunication with the chamber.

39. A combination as set forth in claim 38 which includes an adjustablevalve to control said port.

40. A combination as set forth in claim 1 which includes valve means tobleed air from the hanger to the atmosphere,

said valve means being responsive to the pressure in the hanger to closewhen the pressure is relatively low and to open when the pressure isrelatively high whereby the valve means is closed during initialinflation of the hanger.

41. A combination as set forth in claim 40 in which said valve meanscomprises at least one port in the envelope of the hanger, said portbeing positioned adjacent the upperside of said rigid ring-shaped platethe port being so located that it lies against the plate to be closed bythe plate when the envelope is partially inflated and the envelope peelsaway from the plate to open the port when the envelope approaches fullinflation.

42. A combination as set forth in claim 1 in which a ring-shapedflexible sheet under the rigid ring-shaped plate is attached to therigid ring-shaped plate both adjacent the outer circumferential marginof the ringshaped sheet and adjacent the inner circumferential margin ofthe ring-shaped sheet, the intermediate circumferential portion of thering-shaped sheet bieng slack to permit the annular sealing means tocant locally relative to the rigid ring-shaped plate,

said ring-shaped flexible sheet being vented to the atmosphere.

43. A combination as set forth in claim 1 in which said annular sealingmeans is made largely of resiliently deformable plastic material; I

in which a flexible ring-shaped sheet is interposed between the annularsealing means and the rigid ringshaped plate to act under hoop tensionto oppose rigidly outwardly ballooning of the annular sealing means; and

in which a ring-shaped flexible sheet under the rigid ring-shaped plateis attached to the rigid ringshaped plate adjacent bote the outercircumferential margin of the ring-shaped sheet and the innercircumferential margin of the ring-shaped sheet, the intermediatecircumferential portion of the ring-shaped sheet bien g slack to permitthe annular sealing means to cant locally relative to the rigidring-shaped plate.

44. A combination as set forth in claim 1 in which the hanger is made ofradial segments of woven fabric in which threads of the segments areparallel to the radial center lines of the segments.

45. A combination as set forth in claim 1 in which the sheet material ofthe hanger comprises a blank of sheet material of the generalconfiguration of a truncated cone, the circumferential edge of smallestdiameter of the cone-shaped blank being the inner circumferential edgeof the hanger.

46. A combination as set forth in claim 1 in which support means extendsdownward from the base means to support the base means on the groundsurface when the hanger is deflated,

the overall vertical dimension of the hanger and the annular sealingmeans being such that the annular sealing means is compressed againstthe floor surface when the base means is supported by the base meanswith the hanger deflated 47. A combination as set forth in claim 47 inwhich said support means is surrounded by the hanger and has grooves onits underside to permit radially outward air flow under the supportmeans when air flow is initiated to create the air cushion inside thesealing assembly.

48. A combination as set forth in claim 48 in which said support meansis a chamber in communication with the interior of the hanger and inwhich air is supplied to the hanger through the chamber.

49. A combination as set forth in claim 1 which includes an outer guardmeans surrounding the inflatable hanger and an inner guard meanssurrounded by the in flatable hanger,

the outer circumferential margin of the sheet wall of the hanger beingclamped between the load bearing base and the outer guard means,

the inner circumferential margin of the sheet wall of the hanger beingclamped between the load bearing base and the inner guard means.

1. A fluid cushion device comprising: base means to receive loads, atleast one sealing assembly to confine a fluid cushion, said sealingassembly comprising an annular hanger projecting from the base means andannular structure below the hanger and cooperative therewith to enclosethe fluid cushion, said hanger being made of flexible sheet material andbeing inflatable for vertical resilient deformability to yieldingly urgesaid annular structure away from the base means, said annular structurebeing of less radial dimension than the hanger and being positionedwithin an annular area defined by the hanger, the hanger when inflatedhaving an outer annular flexible sheet wall extending from the basemeans radially inwardly to the annular structure to act under tension tooppose lateral displacement of the annular structure in one respectrelative to the base means, and having an inner annular flexible sheetwall extending from the base means radially outwardly to the annularstructure to oppose lateral displacement of the annular structure in theopposite respect relative to the base means to stabilize the annularstructure relative to the base means without need for linking theannular structure directly to the base means; and means to inflate saidhanger and to supply pressurized fluid to the fluid cushion, saidannular structure including a rigid ring-shaped plate attached to theunderside of the hanger, said annular structure further includingresiliently deformable annular sealing means projecting downward fromthe ring-shaped plate to close proximity to the ground surface under thedevice.
 2. A combination as set forth in claim 1 which includes: guardmeans fixedly mounted on the undersidE of the base to protect theinflatable hanger and to support the base when the hanger is deflated,said guard means including an outer circumferential flange extendingunder the hanger from the outer circumference thereof and an innerannular flange extending under the hanger from the inner circumferencethereof, said two flanges straddling said annular sealing means anddefining an annular opening to permit upward retraction of the annularsealing means when the hanger is deflated to cause the base to besupported by the guard means.
 3. A combination as set forth in claim 2in which said ring-shaped plate overhangs both of said flanges tocooperate with the flanges to shield the inflatable hanger from below.4. A combination as set forth in claim 2 in which said guard meanscomprises: only a central circumferential portion of the rigidring-shaped plate attached to the inflatable hanger so that progressivedownward movement of the rigid ring-shaped plate relative to the basecauses the inflatable hanger to peel away from the rigid ring-shapedplate as the rigid ring-shaped plate approaches its lower limit positionand progressive upward movement of the rigid ring-shaped plateeventually causes the hanger to bulge downward from the rigidring-shaped plate.
 5. A combination as set forth in claim 2 in whichsaid ring-shaped plate is of lesser radial dimension than the inflatablehanger and the guard means provides clearance adjacent both the outercircumferential edge and the inner circumferential edge of thering-shaped plate for downward bulging of the inflatable hanger insidethe guard means.
 6. A combination as set forth in claim 1 in which onlya central circumferential portion of the rigid ring-shaped plate isattached to the inflatable hanger so that progressive downward movementof the rigid ring-shaped plate relative to the base causes theinflatable hanger to peel away from the rigid ring-shaped plate as therigid ring-shaped plate approaches its lower limit position andprogressive upward movement of the rigid ring-shaped plate eventuallycauses the hanger to bulge downward from the rigid ring-shaped plate. 7.A combination as set forth in claim 1 which includes: means to supplycompressed air to the hanger continuously for inflation thereof; andmeans to release air continuously from the hanger at a sufficientlyreduced rate to keep the hanger inflated, whereby any tendency for thehanger to expand and contract for bouncing action is dampened becausethe rate of release of air from the hanger by said releasing meansvaries with the rate of contraction of the hanger.
 8. A combination asset forth in claim 7 in which said means to release air from the hangeris an adjustable valve.
 9. A combination as set forth in claim 7 inwhich the means to supply air to the inflatable hanger comprises anadjustable pressure regulating valve operable to maintain a selectedpressure in the hanger.
 10. A combination as set forth in claim 9 inwhich said means to release air from the hanger is an adjustable valve.11. A combination as set forth in claim 7 in which the annular sealingmeans is inflatable and which includes means to supply compressed aircontinuously to the inflatable annular sealing means for inflationthereof and means to continuously release air from the inflatableannular sealing means at a rate to keep the annular sealing meansinflated.
 12. A combination as set forth in claim 1 in which saidannular sealing means is inflatable and which includes means to keep theannular sealing means inflated.
 13. A combination as set forth in claim12 in which said means to keep the annular sealing means inflatedcomprises means to supply compressed air continuously to the annularsealing means and means to release air continuously from the annularsealing means at a rate to maintain inflation of the annular sealingmeans.
 14. A combination as set forth in claim 13 in which the means tosupply compressed air continuoUsly to the annular sealing meanscomprises an adjustable pressure regulating valve.
 15. A combination asset forth in claim 1 in which said annular sealing means is floatinglymounted on the underside of the rigid ring-shaped plate.
 16. Acombination as set forth in claim 15 in which a ring-shaped flexiblesheet under the rigid ring-shaped plate is attached to the rigidring-shaped plate adjacent at least one of the outer circumferentialmargin and the inner circumferential margin of the ring-shaped sheet,the intermediate circumferential portion of the ring-shaped sheet beingfree from attachment to the ring-shaped plate, the upper annular surfaceof the annular sealing means being bonded to the intermediatecircumferential portion of the ring-shaped sheet.
 17. A combination asset forth in claim 16 in which the ring-shaped flexible sheet isattached to the ring-shaped plate both adjacent the outercircumferential margin of the ring-shaped sheet and the innercircumferential margin of the ring-shaped sheet, the intermediatecircumferential portion of the ring-shaped sheet being slack to permitthe annular sealing means to cant locally relative to the rigidring-shaped plate.
 18. A combination as set forth in claim 1 in whichsaid annular sealing means comprises a stack of substantiallyring-shaped resiliently deformable members; and in which at least oneflexible ring-shaped sheet is interposed between two of said members toact under hoop tension to oppose radially outward ballooning of theannular sealing means.
 19. A combination as set forth in claim 18 inwhich a resiliently flexible wear strip is removably attached to theunderside of the lowest member of the stack.
 20. A combination as setforth in claim 19 in which a flexible abrasive-resistant wear strip ismounted on the underside of the stack; and in which a ring-shapedreinforcement sheet is interposed between the lowermost ring-shapedmember of the stack and said wear strip.
 21. A combination as set forthin claim 18 in which the ring-shaped members of the stack includerelatively thick members made of resiliently deformable cellularelastomer.
 22. A combination as set forth in claim 21 which includes atleast one ring-shaped sheet in hoop tension between two of therelatively thick members of the stack.
 23. A combination as set forth inclaim 1 which includes a wear strip of resilient abrasive-resistantmaterial mounted on the underside of the annular sealing means, saidwear strip being set back radially from the outer circumference of theannular sealing means to minimize noise created by the escaping of airunder the wear strip.
 24. A combination as set forth in claim 23 inwhich the wear strip is made at least largely of elastomeric material.25. A combination as set forth in claim 24 in which the underside of thewear strip is coated with a low friction wear-resistant plastic.
 26. Acombination as set forth in claim 23 in which said wear strip isconstructed of felt-like fabric.
 27. A combination as set forth in claim23 in which the wear strip is releasably mounted by pressure-sensitiveadhesive.
 28. A combination as set forth in claim 23 in which the wearstrip is chamfered along its outer circumferential edge.
 29. Acombination as set forth in claim 23 in which the wear strip ischamfered along its inner circumferential edge.
 30. A combination as setforth in claim 1 in which an upper annular portion of said annularsealing means is resiliently deformable and is substantially softer thanthe remainder of the annular sealing means to cause the annular sealingmeans to accommodate itself to a local rise in the ground surfaceprimarily by compression of said upper annular portion.
 31. Acombination as set forth in claim 30 in which an annular strip ofresilient abrasion-resistant material is mounted on the underside of theannular sealing means, said wear strip being set back radially from theouter circumference of the annular seAling means.
 32. A combination asset forth in claim 30 in which said annular sealing means comprises astack of substantially ring-shaped resilient deformable members, theuppermost of said ring-shaped members being made of cellular elastomer.33. A combination as set forth in claim 32 in which the ring-shapedmembers of the stack below the uppermost member are made of cellularelastomer.
 34. A combination as set forth in claim 1 in which a centralconcentric annular portion of the envelope of the hanger is united witha corresponding ring-shaped sheet and the ring-shaped sheet in turn isbonded to the upper surface of the rigid ring-shaped plate.
 35. Acombination as set forth in claim 1 in which a cylindrical wall extendsdownward from the base means adjacent the inner periphery of theinflatable hanger and in which the inner peripheral edge of the envelopeof the hanger is attached to said cylindrical wall at a level spacebelow the base means to increase the effective volume of the envelope.36. A combination as set forth in claim 1 which includes a chamber onthe underside of the base means, said hanger surrounding the chamber andbeing in fluid communication with the chamber for air flow between thechamber and the hanger.
 37. A combination as set forth in claim 36 whichincludes a passage extending downward from the base means to supply airto the air cushion; in which said chamber is an annular chambersurrounding said passage; and in which said passage is in communicationwith said chamber to supply air to the hanger through the chamber.
 38. Acombination as set forth in claim 37 in which the wall of said passagehas a port for full communication with the chamber.
 39. A combination asset forth in claim 38 which includes an adjustable valve to control saidport.
 40. A combination as set forth in claim 1 which includes valvemeans to bleed air from the hanger to the atmosphere, said valve meansbeing responsive to the pressure in the hanger to close when thepressure is relatively low and to open when the pressure is relativelyhigh whereby the valve means is closed during initial inflation of thehanger.
 41. A combination as set forth in claim 40 in which said valvemeans comprises at least one port in the envelope of the hanger, saidport being positioned adjacent the upper side of said rigid ring-shapedplate the port being so located that it lies against the plate to beclosed by the plate when the envelope is partially inflated and theenvelope peels away from the plate to open the port when the envelopeapproaches full inflation.
 42. A combination as set forth in claim 1 inwhich a ring-shaped flexible sheet under the rigid ring-shaped plate isattached to the rigid ring-shaped plate both adjacent the outercircumferential margin of the ring-shaped sheet and adjacent the innercircumferential margin of the ring-shaped sheet, the intermediatecircumferential portion of the ring-shaped sheet bieng slack to permitthe annular sealing means to cant locally relative to the rigidring-shaped plate, said ring-shaped flexible sheet being vented to theatmosphere.
 43. A combination as set forth in claim 1 in which saidannular sealing means is made largely of resiliently deformable plasticmaterial; in which a flexible ring-shaped sheet is interposed betweenthe annular sealing means and the rigid ring-shaped plate to act underhoop tension to oppose rigidly outwardly ballooning of the annularsealing means; and in which a ring-shaped flexible sheet under the rigidring-shaped plate is attached to the rigid ring-shaped plate adjacentboth the outer circumferential margin of the ring-shaped sheet and theinner circumferential margin of the ring-shaped sheet, the intermediatecircumferential portion of the ring-shaped sheet being slack to permitthe annular sealing means to cant locally relative to the rigidring-shaped plate.
 44. A combination as set forth in claim 1 in whichthe hanger is made of radial segments of woven fabric in which threadsof the segments are parallel to the radial center lines of the segments.45. A combination as set forth in claim 1 in which the sheet material ofthe hanger comprises a blank of sheet material of the generalconfiguration of a truncated cone, the circumferential edge of smallestdiameter of the cone-shaped blank being the inner circumferential edgeof the hanger.
 46. A combination as set forth in claim 1 in whichsupport means extends downward from the base means to support the basemeans on the ground surface when the hanger is deflated, the overallvertical dimension of the hanger and the annular sealing means beingsuch that the annular sealing means is compressed against the floorsurface when the base means is supported by the base means with thehanger deflated.
 47. A combination as set forth in claim 46 in whichsaid support means is surrounded by the hanger and has grooves on itsunderside to permit radially outward air flow under the support meanswhen air flow is initiated to create the air cushion inside the sealingassembly.
 48. A combination as set forth in claim 47 in which saidsupport means is a chamber in communication with the interior of thehanger and in which air is supplied to the hanger through the chamber.49. A combination as set forth in claim 1 which includes an outer guardmeans surrounding the inflatable hanger and an inner guard meanssurrounded by the inflatable hanger, the outer circumferential margin ofthe sheet wall of the hanger being clamped between the load bearing baseand the outer guard means, the inner circumferential margin of the sheetwall of the hanger being clamped between the load bearing base and theinner guard means.